Year	mmol per litre
1980	5.329
1981	5.313
1982	5.299
1983	5.284
1984	5.269
1985	5.252
1986	5.238
1987	5.221
1988	5.202
1989	5.179
1990	5.152
1991	5.119
1992	5.067
1993	5.017
1994	4.972
1995	4.936
1996	4.901
1997	4.87
1998	4.845
1999	4.825
2000	4.81
2001	4.799
2002	4.795
2003	4.792
2004	4.793
2005	4.794
2006	4.795
2007	4.799
2008	4.801